January 7, 2009

Black Holes May Have Formed Before Galaxies

Black holes may have come before the formation of galaxies, astronomers reported on Wednesday, adding information that could provide new insights into the nature of the mysterious invisible black objects.

At the  213th meeting of the American Astronomical Society in Long Beach, California, researchers said they discovered a clear link between the mass of a black hole and the galaxy where it was spotted.

"It looks like the black holes came first. The evidence is piling up," said Chris Carilli, of the National Radio Astronomy Observatory (NRAO).

Using the Very Large Array telescope in Chile, the international team of astronomers noted that the ratio of the black hole and the bulge mass is nearly the same for a wide range of galactic sizes and ages.

"This constant ratio indicates that the black hole and the bulge affect each others' growth in some sort of interactive relationship," said Dominik Riechers, of Caltech. "The big question has been whether one grows before the other or if they grow together, maintaining their mass ratio throughout the entire process."

The Very Large Array telescope, as well as the Plateau de Bure Interferometer in France has provided astronomers with a far-seeking glimpse back into the history of the Universe "“ some 13.7 billion years ago.

"We finally have been able to measure black-hole and bulge masses in several galaxies seen as they were in the first billion years after the Big Bang, and the evidence suggests that the constant ratio seen nearby may not hold in the early Universe," said Fabian Walter of the Max-Planck Institute for Radioastronomy (MPIfR) in Germany.

"The black holes in these young galaxies are much more massive compared to the bulges than those seen in the nearby Universe."

Walter says this suggests that black holes formed before galaxies.

Now astronomers will focus on determining how the black hole and the bulge affect each others' growth.

"We don't know what mechanism is at work here, and why, at some point in the process, the 'standard' ratio between the masses is established," Riechers said.

The planned development of the Expanded Very Large Array (EVLA) in New Mexico and the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile may provide researchers with more pieces of the puzzle.

"The Expanded Very Large Array (EVLA) and the Atacama Large Millimeter/submillimeter Array (ALMA) will give us dramatic improvements in sensitivity and the resolving power to image the gas in these galaxies on the small scales required to make detailed studies of their dynamics," said Carilli.

"With the new observatories we'll have in the next few years, we'll have the opportunity to learn important details from the era when the Universe was only a toddler compared to today's adult," he added.


Image 1: In this top-down illustration of a black hole and its surrounding disk, gas spiraling toward the black hole piles up just outside it, creating a traffic jam. The traffic jam is closer in for smaller black holes, so X-rays are emitted on a shorter timescale. Credit: NASA

Image 2: VLA image (right) of gas in young galaxy seen as it was when the Universe was only 870 million years old. CREDIT: NRAO/AUI/NSF, SDSS


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